Cinebench 8800gt benchmarks all over the map

[kudukudu]

I decided to see how leopard would handle games and fired up unreal tournament 2004. It ran fine for a while, but then I noticed there was a lot of jitter in the graphics. I closed the program and then noticed that even general GUI behavior like bringing up spaces seemed really slow. I downloaded Cinebench and and ran the opengl benchmark. The 8800gt only came up at 2100 CB-GFX. I then did a reboot and the benchmark came in at around 6600 CB-GFX or something like that. Can this type of behavior simply be attributed to early/buggy drivers (e.g. don't worry this won't be a problem in 6 months) or is this something that might suggest a more serious problem?